An amputee is a person who has lost part of an extremity or limb such as a leg or arm which commonly may be termed as a residual limb. Residual limbs come in various sizes and shapes with respect to the stump. That is, most new amputations are either slightly bulbous or cylindrical in shape while older amputations which may have had significant atrophy are generally more conical in shape. Residual limbs may further be characterized by their various individual problems or configurations including the volume and shape of a stump and possible scar, skin graft, bony prominence, uneven limb volume, neuroma, pain, edema or soft tissue configurations.
Prosthetic and orthotic devices provide mobility and functionality to amputees, but must be secured to a residual limb to do so. Many devices include sockets configured for reception of the residual limb. Because the size and shape of a residual limb may vary among amputees, and even for one amputee over days or years of prosthetic wear, creating vacuum between the surface of the residual limb (or a sock, elastomeric liner, or sheath covering the limb) and the socket to keep the prosthetic device from loosening or disconnecting from the stump is beneficial for an amputee.
The use of vacuum to attach an artificial limb to a residual limb (i.e., vacuum suspension) offers many advantages over more traditional means of artificial limb retention such as straps, retaining pins attached to a liner covering the limb, and suction type sockets which do not use a vacuum pump. When the entire socket/limb interface is subject to high levels of vacuum, the benefits include exceptional retention with no detectable movement between the residual and artificial limbs, residual limb volume management, increased proprioception, and improved circulation accompanied by a reported increased rate of wound healing on the residual limb.
Both electric and mechanical vacuum pumps are available for prosthetic use. The most common designs implement a moving wall to generate vacuum. Electric pumps typically employ a diaphragm-like moving wall which is driven up and away from a surface. As the diaphragm is pulled away from the surface air is pulled into a vacuum chamber created between the surface and the diaphragm. An electric pump may advantageously consume none of the available space between the socket and the foot, and they are also always “on,” so the vacuum level does not rely on walking or other movement by an amputee and will not drop below a selected level unless a leak occurs which exceeds the capacity of the pump or the battery of the pump is depleted. However, they may have batteries to recharge, are susceptible to impact damage, and may be difficult to position on the limb.
Mechanical pumps, on the other hand, are weight-activated rather than electrically powered. Mechanical pumps are also durable and have a high resistance to impact forces. A mechanical pump does not require recharging and can incorporate additional prosthetic functions, such as vertical shock absorption and rotation, at the cost of taking up available space between the socket and the end of the limb. Tall foot designs are typically more comfortable and natural-feeling for the amputee than shorter foot designs, but the length of the mechanical pump reduces the height available for a prosthetic foot or other components for the limb. Furthermore, if the pump has large vertical deflection between extension and compression, the amputee's gait may be negatively unbalanced.
Additionally, none of the benefits of vacuum suspension exist until significant vacuum is created since the socket will not be firmly connected to the residual limb. This means an amputee using a mechanical pump as part of a vacuum-retained artificial limb must cycle the pump repeatedly to create vacuum before attempting to use the artificial limb, whether after donning the limb or after intentionally releasing the vacuum. This may be frustrating and time consuming. Vacuum limbs also have various potential leak sources and vacuum will often bleed off after a period of inactivity. Therefore, there is a need for improvements in vacuum suspended artificial limbs and orthotics.